2
High availability technologies
As previously mentioned, increasing MTBF or decreasing MTTR can enhance the availability of a
network. The high availability technologies described in this section meet the level 3 high availability
requirements by decreasing MTTR.
High availability technologies can be classified as fault detection technologies or protection switchover
technologies.
Fault detection technologies
Fault detection technologies enable detection and diagnosis of network faults. CFD, DLDP, and Ethernet
OAM are data link layer fault detection technologies. NQA is used for diagnosis and evaluation of
network quality. Monitor Link and Track work along with other high availability technologies to detect
faults through a collaboration mechanism. For more information about these technologies, see Table 2.
Table 2 Fault detection technologies
Connectivity Fault Detection (CFD), which conforms to IEEE
802.1ag Connectivity Fault Management (CFM) and ITU-T
Y.1731, is an end-to-end per-VLAN link layer Operations,
Administration and Maintenance (OAM) mechanism used for
link connectivity detection, fault verification, and fault location.
CFD configuration in
the High Availability
Configuration Guide
The Device link detection protocol (DLDP) deals with
unidirectional links that may occur in a network. Upon detecting
a unidirectional link, DLDP, as configured, can shut down the
related port automatically or prompt users to take actions to
avoid network problems.
DLDP configuration in
the High Availability
Configuration Guide
As a tool monitoring Layer 2 link status, Ethernet OAM is mainly
used to address common link-related issues on the “last mile”.
You can monitor the status of the point-to-point link between two
directly connected devices by enabling Ethernet OAM on them.
Ethernet OAM
configuration in the
High Availability
Configuration Guide
Network Quality Analyzer (NQA) analyzes network
performance, services and service quality through sending test
packets, and provides you with network performance and
service quality parameters such as jitter, TCP connection delay,
FTP connection delay and file transfer rate.
NQA configuration in
the Network
Management and
Monitoring
Configuration Guide
Monitor link is a port collaboration function. It is usually used in
conjunction with Layer 2 topology protocols. The idea is to
monitor the states of uplink ports and adapt the up/down state
of downlink ports to the up/down state of uplink ports,
triggering link switchover on the downstream device in time.
Monitor link
configuration in the
High Availability
Configuration Guide
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